This invention relates generally to apparatus for storing at least two substances, one of which is a radioactive substance, and to a related method of injecting the radioactive substance into a well with such an apparatus. More particularly, but not by way of limitation, the present invention relates to a dual fluid transportation assembly and method for storing and transporting a radioactive liquid and a diluting liquid in a single container and for subsequently storing in the assembly waste products comprising a mixture of the two substances.
Sometimes during oil or gas well fracturing operations, a radioactive fluid is injected into the fracturing fluid being pumped downhole. Such a radioactive fluid either gets trapped in the earthen formation or is deposited on the surface of the formation. Subsequent gamma ray logging operations will then locate where this radioactive "tracer" fluid is trapped in or deposited on the formation. The information from this logging operation is then used to determine where a fracture is created, its depth, its type, the aggregate number of fractures, an estimation of the fracture thickness, and the effectiveness of the fracturing method used.
In performing such a fracturing job wherein a liquid radioactive fluid is used, it has been typical to transport several small containers (e.g., ones having storage capacities of ten cubic centimeters) of radioactive tracer to the well site where the contents of the small containers are dumped into a fluid reservoir at the site. Such small containers have been glass bottles which have threaded screw caps attached and which are protectively housed during transportation in respective lead casings. Once such assemblies arrive at the well site, however, the unshielded bottles are removed and manipulated to pour their contents into the fluid reservoir, where the tracer is diluted from its stored concentrated form prior to being pumped through the tracer injection equipment.
Shortcomings of this technique include the risk of human, equipment and environmental contamination which can relatively easily occur either if humans directly handle the unprotected bottles of concentrated radioactive fluid or if they handle them indirectly with mechanical tongs or other extra equipment at the well site. When such a dangerous substance is handled by either manner at the well site itself, there is a relatively high risk of spillage due to mishandling of the container and due to less than ideal weather conditions. Although the risk of direct contamination of humans may be reduced by using a mechanical handling device, the risk of spillage, and thus of environmental contamination, may be higher with respect to the use of such mechanical equipment because such mechanical handling is likely less sensitive and controllable than direct human handling. The risk of direct human contamination would be greater through such direct handling, however, since the bottles are not shielded when they are removed from their lead casings to transfer the fluid, particularly when the contents of the bottles have the high radioactivity levels that can be associated with the concentrated types of radioactive substances used and when such substances are highly absorbable.
A further disadvantage of the aforementioned technique is that contaminated bottles remain after their contents have been poured into the fluid reservoir. There can be numerous such bottles at the well site if a large quantity of tracer is needed because of the small individual quantities of each bottle.
Additionally, the use of a separate fluid reservoir located at the well site presents another potential hazard because it may be a large open tank or other receptacle which may not be suitable for adequate containment of radioactive substances. Furthermore, such a separate reservoir can become contaminated once the radioactive substance is poured into it, and the rest of the equipment by which the diluted radioactive substance is pumped into the well can become similarly contaminated. Such contaminated equipment presents radioactivity exposure and contamination risks to humans and the environment.
The last-mentioned shortcoming of contaminated equipment is particularly significant with respect to the typical radioactive tracer injection system currently being used in the oil industry because in such a system, the tracer fluid is metered from the reservoir, into which the tracer has first been added (which transfer is itself subject to significant risk), to the suction inlets of high pressure fracturing pumps which are not necessarily dedicated solely for radioactive use. Because usage with radioactive tracers can contaminate such pumps, the pumps must be appropriately cleaned or disposed of to avoid subsequent risks of exposure or contamination. This is difficult to control since such pumps are not necessarily dedicated to only one well site or to only one injection or fracturing job. Thus, aside from the significant human health hazards arising from such equipment, such contaminated equipment can lead to the pertinent governmental regulatory body issuing citations, imposing fines, and revoking licenses.
Even assuming proper handling of the small glass bottle containers and the injection equipment, there is the significant additional risk arising from the contaminated waste fluids often remaining after such an injection job, but for which there may be no adequate disposal containers provided. Thus, proper disposal equipment must also be provided at the well site to reduce the chances of the waste fluids being improperly and unsafely dumped into the environment.
In view of the shortcomings of this small glass bottle/separate reservoir and disposal equipment/contaminated injection system by which radioactive tracer substances are injected into a well, such as during fracturing operations, there is the need for a new type of radioactive substance container to transport the substance safely and to overcome the problems arising from the use of a separate fluid reservoir at the well site (into which the tracer substance has heretofore been transferred under whatever weather conditions existed at the well site) and from the contamination of the injection equipment and from the need to dispose of contaminated waste substances. Such a need could be satisfied by a single multiple-reservoir container for holding both the concentrated radioactive substance and the diluting substance which would otherwise be contained in the separate external fluid reservoir. Such a container should have a significantly increased storage capacity over the small glass bottle containers so that only one, or at most only a few, containers are needed at the well site to reduce the handling of the substances and their containers. Such a container should also be constructed so that transfers of the radioactive substance can be made within a closed system to prevent weather conditions at the well site from affecting the transfer and to otherwise prevent or reduce the risk of spillage. Additionally, such a container needs to be constructed to meet pertinent regulatory requirements, such as those pertaining to containers by which radioactive substances are transferred from or to locations remote from the well site.
In addition to the foregoing needs pertaining particularly to the container, there is the further need for a system, including a method, by which such a novel container is used to avoid contaminating the injection equipment found at the well site, which equipment may be needed for other purposes.